Two different processes for grinding and wheels therefor are known in the art. For precise grinding on metal, ceramic and other materials, a mechanical grinding method with grindstones made of particles of green carborundum, white alundum, diamond, boron nitride and the like is widely used. This mechanical method, however, has some shortcomings. They are:
1. A low grinding speed is required.
2. It is almost impossible to grind ultra hard alloy, hardened steel by quenching, sendust alloy and rare earth compound.
3. The strain created during the process may cause deformation of the work.
4. The grindstone wears down quickly.
For grinding hard-to-process materials, the electrolytic method, in which a grindstone made solely of graphite works as an electrode, has been in use for some time. With the help of a proper electroconductive grinding lubricant, this method allows electricity to pass from the grindstone made of graphite to the material to be ground. This electrochemically erodes and dissolves the material. With this method, the ability to process a certain material depends on the material's electric and electro-chemical properties, and not on its mechanical properties. Thus, with this grinding wheel, it is possible to grind a material which is almost impossible to grind using strictly the mechanical method. Yet, there are some disadvantages which are as follows:
1. Because the electroconductive grinding lubricant prevents direct contact between the grindstone and the work, it is hard to get smooth and precise results.
2. In order to get a high degree of accuracy, finish grinding has to be done using the mechanical method.
3. Therefore, the rapid grinding speed, which is an advantage of the electrolytic method, cannot be fully realized.
A grindstone made of porous green carborundum having electroless copper plating applied thereto, making it electrically conductive, has also been in use. This prior art grindstone is made by pressure impregnating a copper aqueous solution into the porous green carborundum. With this grindstone, mechanical and electrolytic grinding can be performed at the same time. But, this method also has its shortcomings, which are as follows:
1. Because the electrical conductivity may vary with the passage of time, it is hard to maintain the optimum electrolytic condition during grinding.
2. Because the porous grindstone is made by impregnating plating fluid into the grindstone, the grindstone itself is brittle and wears down easily.
3. It is not easy to make a grindstone of this type without chips and cracks. It is especially hard to make a thin blade grindstone of this kind.
4. With this method alone, an exact and smooth finish is not attainable.
5. Since mechanical grinding is required for the finishing, pressure from the grindstone may cause the deformation of the work during or after the grinding process.
The present invention aims at overcoming the aforementioned shortcomings. It does so by a new, efficient, and durable grinding wheel which will not easily wear down or crack, and which will not cause deformation of the work. It can also attain a higher degree of accuracy and a superior finish without additional mechanical grinding.
The grinding wheel of the present invention has a circumferential rim and a plurality of electrically conductive zones and non-conductive grinding zones therebetween around the rim.
The wheel can comprise an annular electro-conductive tube, an annular grindstone radially surrounding the tube, a plurality of axial grooves filled with an electro-conductive material on the rim of the grindstone, and connector means extending radially from the tube to the filled axial grooves for electrically connecting the grooves with the tube. The filled axial grooves are the conductive zones and the portions of the grindstone therebetween are the grinding zones.
The connector means can comprise side grooves on the sides of the grindstone filled with an electro-conductive material The conductor means alternatively can comprise an annular electroconductive disk imbedded in the grindstone extending from the tube to the axial grooves. The axial grooves can be parallel to the axis of the grindstone and the side grooves can follow the radii of the grindstone. Alternatively, the axial grooves can be offset-angled at an acute angle from the axis and the side grooves can be offset-angled at an acute angle from the radii of the grindstone.
The wheel can further comprise a pair of annular, electro-conductive disks concentrically mounted on opposite sides of the grindstone electrically connected to the tube and the side grooves.
The wheel can comprise an annular electro-conductive tube and an annular grindstone radially surrounding the tube having selective sector-shaped portions impregnated with an electro-conductive material. These impregnated portions are the conductive zones and the portions therebetween are the grinding zones.
Alternatively, the wheel can comprise an annular electro-conductive tube, a grindstone treated so as to be electro-conductive radially surrounding the tube, and a plurality of axial grooves on the rim of the grindstone filled with an insulating material. The filled axial grooves are the grinding zones and that portions of the grindstone therebetween are the conductive zones.
The wheel can comprise an annular wheel of a conductive substance having an outer circumference, a plurality of electroconductive grindstone segments curved to fit and mounted on the circumference with radially extending gaps between adjacent segments, and insulating material filling the gaps. In this embodiment, the insulating material filling the gaps are the grinding zones and the segments are the conductive zones.
The wheel can comprise an annular wheel of electroconductive substance having an outer circumference and a plurality of radially extending teeth and a plurality of grindstone segments curved to fit and mounted on the circumference between the teeth. The adjacent segments are separated from one another by the teeth. In this embodiment, the teeth are the conductive zones and the segments are the grinding zones.
The wheel can comprise an annular electroconductive tube and an annular grindstone radially surrounding the tube having a circumference and a plurality of radial grooves extending from the tube to the circumference. The grooves can be filled with an electroconductive material. The portions of the filled grooves in this embodiment on the circumference are the conductive zones and the portions of the grindstone surrounding the grooves on the circumference are the grinding zones.
The wheel can also comprise an annular conductive tube and an annular electroconductively treated grindstone having a circumference and a plurality of radial grooves extending from the tube to the circumference. The grooves can be filled with an insulating material. In this embodiment, the portions of the filled grooves on the circumference are the grinding zones and the portions of the electroconductively treated grindstones surrounding the grooves on the circumference are the conductive zones.
The grooves in the above-two-mentioned embodiments can be formed on both sides of the grindstone and can be rectangular in cross-section. The grooves could also be triangular in crosssection. Alternatively, the grindstone has opposed faces and a center portion therebetween with the grooves formed in the center portion extending to the circumference.
The present invention also comprises a method of grinding a workpiece comprising mounting a grinding wheel having a circumferential rim and a plurality of electrically conductive zones and non-conductive grinding zones therebetween around the rim on a grinding machine, applying electricity to the conductive zones, and simultaneously spinning the wheel and spraying an electrolytic fluid on the wheel while applying the workpiece to the wheel. Alternatively, the wheel can be applied to the workpiece.
The present invention also includes a method of manufacturing a grinding wheel comprising forming an annular grindstone of abrasive particles having opposed side, a circumferential rim, and a center aperture, fitting an annular conductive tube into the aperture, and making a plurality of alternating electrically conductive zones and non-conductive grinding zones around the rim with the conductive zones being electrically connected to the tube.
The above step of making can comprise cutting a plurality of axial grooves in the rim, filling the axial grooves with an electroconductive material, and connecting the filled axial grooves to the tube. The connecting can be accomplished by cutting a plurality of radial side grooves from the tube to the axial grooves and filling these radial grooves with an electro-conductive material. The connecting can also comprise imbedding a pair of annular electroconductive disks into the opposed sides with the disks extending radially from the tube to the axial grooves. The step of connecting could also comprise dividing the grindstone radially into two halves, and inserting an annular electroconductive disk between the halves extending from the tube to the axial grooves.
In another embodiment, the making can comprise treating a plurality of sector-shaped zones of the grindstone to make the same electroconductive with the sector-shaped zones extending to meet the tube. This treating can comprise masking selected portions of the opposed sides and the rim leaving there the desired sector-shaped zones, placing the masked grindstone into a vacuum chamber dividing the chamber into two portions, placing an aqueous solution of the electroconductive material into one of the portions, drawing a vacuum in the other portion thereby impregnating the aqueous solution into the sector-shaped zone, drying the selectively impregnated grindstone, and stripping the masking from it.
The step of making in another embodiment can comprise treating the entire grindstone to make the same electroconductive, cutting a plurality of axial grooves in the rim of the grindstone and filling the grooves with an insulating material.
The step of making could also comprise dividing the grindstone into a plurality of curved segments, treating the segments to make the same electroconductive, mounting the segments onto the tube with gaps between adjacent segments, and filling the gaps with an insulating material. Further, the step of making can comprise forming a plurality of radial grooves in the grindstone from the tube to the rim, and filling the grooves with either an electroconductive material or an insulating material. In the case where the grooves are filled with an insulating material, the grindstone is previously treated to make the same electroconductive. The grooves can be cut into either both opposed sides or can be formed in a center portion between the opposed sides.
A further method of making a grinding wheel can comprise forming a wheel of electroconductive substance having a circumferential rim and a plurality of radially extending teeth, forming a plurality of grindstone segments of abrasive particles which are curved to fit the rim, and mounting the segments of abrasive particles which are curved to fit the rim, and mounting the segments onto the rim with each segment being separated from adjacent segments by one of the teeth.
The abrasive particles that these grindstones can be made of can be selected from the group consisting of green carborundum, white alundum, diamond, boron nitride, boron carbide, tungsten carbide, titanium carbide, titanium nitride, tantillum carbide, and niobium carbide. Other suitable materials would be readily apparent to those having ordinary skill in the art.